Prion diseases, also known as transmissible spongiform encephalopathies (TSEs), are a group of rare, invariably fatal neurodegenerative disorders characterized by the misfolding and self-propagation of the cellular prion protein (PrP^C) into an abnormal, protease-resistant isoform (PrP^Sc). This unique disease mechanism, discovered by Stanley Prusiner (Nobel Prize 1997), demonstrated that a protein alone—without nucleic acids—can act as an infectious agent [1].
Prion diseases affect both humans and animals and include:
- Creutzfeldt-Jakob Disease (CJD) — Sporadic, familial, iatrogenic, and variant forms
- Fatal Insomnia (FI) — Familial and sporadic variants
- Kuru — Historical epidemic in Papua New Guinea
- Gerstmann-Sträussler-Scheinker syndrome (GSS)
The central event in prion diseases is the conformational conversion of the normal cellular prion protein (PrP^C) to the disease-associated isoform (PrP^Sc):
| Feature |
PrP^C (Normal) |
PrP^Sc (Disease) |
| Structure |
α-helical (40% helix) |
β-sheet (40-50% sheet) |
| Solubility |
Detergent soluble |
Detergent insoluble |
| Protease resistance |
Sensitive |
Partial resistance |
| Aggregation |
None |
Forms amyloid fibrils |
| Cellular function |
Neuroprotective |
Toxic |
PrP^Sc acts as a template for the conversion of PrP^C [2]:
- Contact: PrP^Sc contacts normal PrP^C
- Conversion: Conformational change induced
- Aggregation: PrP^Sc molecules aggregate
- Replication: More PrP^Sc is produced
- Spread: Throughout nervous system
Prion strains exhibit different biological properties:
- Distinct incubation periods: Vary from weeks to years
- Different neuropathology: Regional specificity varies
- Species barriers: Transmission between species differs
- Incidence: 1-2 per million annually
- Age: Typically 60-70 years
- Progression: Rapid decline over weeks to months
| Symptom |
Frequency |
| Dementia |
100% |
| Myoclonus |
80% |
| Cerebellar signs |
60% |
| Cortical blindness |
20% |
| Pyramidal signs |
50% |
- Cause: Mutations in PRNP gene
- Inheritance: Autosomal dominant
- Penetrance: Variable (40-100%)
- Transmission: Contaminated growth hormone, dura mater grafts
- Incubation: 5-30 years
- Prevention: Screening measures implemented
- Cause: Bovine spongiform encephalopathy (BSE) exposure
- Age: Younger onset (average 28 years)
- Psychiatric symptoms: Prominent early
- Duration: Longer (12-14 months)
- Mutation: D178N with methionine at codon 129
- Primary symptom: Progressive insomnia
- Autonomic dysfunction: Hyperthermia, hypertension
- Duration: 7-36 months
- Sporadic: No PRNP mutation
- 129MM genotype: Predisposes
- Clinical course: Similar to FFI
| Marker |
sCJD |
vCJD |
Other TSEs |
| 14-3-3 protein |
Positive |
Variable |
Variable |
| Total tau |
Elevated |
Elevated |
Normal/elevated |
| Neurofilament light |
Elevated |
Elevated |
Variable |
| PrP^Sc detection |
Positive |
Positive |
Positive |
- Periodic sharp wave complexes (PSWC): Characteristic in sCJD
- Sensitivity: 60-80% in sCJD
- Timing: Usually appear mid-disease
| Modality |
Finding |
| MRI FLAIR/DWI |
Cortical ribboning, basal ganglia hyperintensity |
| PET |
Hypometabolism |
| SPECT |
Reduced perfusion |
- Definitive diagnosis: Detection of PrP^Sc by immunohistochemistry
- Sensitivity: ~95% in sCJD
- Used when: Diagnosis uncertain
- Useful for vCJD: PrP^Sc in lymphoid tissue
- Not useful for sCJD: Limited sensitivity
| Route |
Example |
| Dietary |
BSE-contaminated beef |
| Iatrogenic |
Growth hormone, dura mater |
| Blood |
vCJD transmission reported |
| Direct |
Kuru (ritualistic cannibalism) |
| Genetic |
PRNP mutations |
The species barrier effect explains why prions don't readily jump between species:
- PrP sequence homology: Similarity between species
- PrP^Sc conformation: Strain-specific effects
- Inoculum dose: Higher doses increase transmission
- vCJD: 4 transfusion-associated cases reported
- Screening: Blood donor deferral implemented
- Detection: PrP^Sc detection methods in development
No effective disease-modifying therapy exists for any prion disease.
| Compound |
Mechanism |
Trial Status |
| Pentosan polysulfate |
Anti-prion activity |
No benefit |
| Quinacrine |
PrP^Sc aggregation inhibitor |
Failed |
| Flupirtine |
Neuroprotective |
No benefit |
| Doxcycline |
Anti-prion |
Failed |
- Anti-PrP antibodies: Immunotherapy approaches
- Gene silencing: ASO targeting PRNP
- PrP^Sc clearance: Pharmacological agents
- Stem cell therapy: Neuronal replacement
- Multidisciplinary approach: Management of symptoms
- Nutritional support: As dysphagia develops
- Infection prevention: Urinary catheter care
- Palliative care: Early involvement recommended
- Standard precautions: For patient contact
- Decontamination: Sodium hydroxide, bleach
- Single-use equipment: Where possible
- Blood donor deferral: For at-risk individuals
- BSE surveillance: In cattle populations
- Feed bans: Preventing cross-species transmission
- Screening: Blood and tissue donations
- Prusiner SB (1998) Proc Natl Acad Sci 95(23):13363-13383 — Prion diseases review
- Aguzzi A et al. (2008) Annu Rev Pathol 3:11-40 — Prion biology
- Collinge J (2010) Annu Rev Neurosci 33:299-325 — Prion mechanisms
- Hill AF et al. (2003) Brain 126(Pt 6):1333-1346 — Diagnosis of CJD
- Mead S et al. (2009) Lancet 374(9702):178-183 — Genetics of prion disease
- Brown P et al. (2006) Lancet 367(9528):2068-2074 — vCJD
- Cortelli P et al. (2006) Brain 129(Pt 9):2270-2280 — Fatal insomnia
- Geschwind MD (2015) Continuum 21(6):1612-1638 — Prion disease diagnosis